Materials with nanometer dimensions, defined as having at least one dimension less than about 100 nm, have received steadily growing interest due to their unique properties and application potential, oftentimes superior to their bulk counterparts. Examples include zero-dimensional nanoparticle (1), one-dimensional nanowires (2-4), and two-dimensional (2D), graphenes (5-7). Because of the quantum confinement of electrons in one or more dimensions, novel electrical, optical, and magnetic properties can be achieved in nanostructures. Currently, carbonaceous nanomaterials such as carbon nanotubes (CNTs), graphene, graphene oxides, graphite sheets, carbon nanodots hold the most promise among nanoscale materials.
In particular, carbon nanotubes are categorized as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). SWCNTs can be conceptualized by rolling a single sheet of graphene into a seamless cylinder; whereas MWCNTs consist of multiple rolled layers (concentric tubes) of graphene. Depending on the chirality along the graphene sheet, either semiconducting or metallic electronic states are created (8). Both experiments and theory have shown that SWCNTs possess high mobility (on the order of 100000 cm2 V−1 s−1) (9), high conductivity (up to 400000 S cm−1), and, for semiconducting nanotubes, tube diameter-dependent band gap (Egap≈1/Rtube) (10).
Physical properties and device integration of individual nanoscale materials have been widely studied, while thin films of nanoscale materials is an emerging research area, with the advantage of statistical averaging for better reproducibility (11). Collective behavior of nanostructures can provide unique physical properties and enhanced device performance. A 2D network, often referred to as a thin film, made of randomly distributed CNTs can be regarded as a novel material. Because of the mixture of metallic and semiconducting nanotubes, CNT thin films show a semiconductor-metal transition as the film thickness increases (12). However, several techniques have been developed to isolate the semiconducting nanotubes, making CNTs a viable material for transistor applications. Thus, there are now numerous studies on nanotube thin films. For example, CNT thin films with density close to the percolation threshold show semiconductor behavior and can be used as the active layer in thin film transistors (3, 4, 13-18). However, most of these devices operate at very large voltages because the gate dielectric does not have a large capacitance (18).
Accordingly, there is a need in the art for thin film transistor devices where the thin film semiconductor is prepared from carbonaceous nanomaterials and where the gate dielectric material can enable device operation at low operating voltages.